Photocurable materials are commonly used in dentistry as sealants, adhesives, and as filler material for filling dental cavities. To cure the photocurable material, it is exposed to radiant energy in a preselected spectral range, typically in either the long-wave ultraviolet or blue visible spectrum, tailored to the composition of the photocurable material. A light-curing unit containing a reflector lamp is used to irradiate the photocurable material by directing light from the reflector lamp through a light guide positioned with its distal end adjacent to the photocurable material to be cured. The light guide functions to channel the light to the material at the site of the dental restoration.
The physics of the transmission of light through a light conductor is well known, and is not unique to the field of dentistry. Any conventional text on optics will provide the fundamentals to compute the critical angle and the numerical aperture for maximum transmission of light through a conductive medium of known geometry, composition, and refractive index. It is the result of practical factors, such as limited accessibility, maneuverability, and size, that complicates the design of a dental light guide and light-curing unit. For example, to provide maximum accessibility and maneuverability within the oral cavity of a patient, the dental practitioner requires the light guide to have a curved end section. Substantial emphasis has been given to the design of a light guide to maximize the transmission of light from a reflector lamp of given dimensions operating at a given voltage rating under the constraints imposed by the dental practitioner and practical considerations of length and diameter.
The conventional light guide is a solid conductor of either glass or plastic, or is composed of a fiber optic conductor consisting of multiple strands of glass fiber held together as a flexible bundle or fused into a solid rod of individual fibers.